Optical: systems and elements – Image stabilization – By movable refractive structure
Reexamination Certificate
2000-12-14
2002-07-23
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Image stabilization
By movable refractive structure
C359S554000, C359S689000, C359S692000
Reexamination Certificate
active
06424465
ABSTRACT:
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 11-355880, filed Dec. 15, 1999
Japanese Patent Application No. 2000-187228, filed Jun. 22, 2000
Japanese Patent Application No. 2000-370847, filed Dec. 6, 2000
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a front tele-converter, and more particularly to a front tele-converter mounted on the object side of a photo-taking lens in order to enlarge its focal length, and also relates to its vibration-reduction technique.
2. Related Background Art
Front tele-converters conventionally used for video cameras are disclosed in, e.g., Japanese Patent Application Laid-open No.63-210810 and No.3-59508.
Vibration-reduction techniques for front tele-converters are also disclosed in Japanese Patent Publication No.7-119902 and Japanese Patent Application Laid-open No.9-171205.
The front tele-converter disclosed in Japanese Patent Application Laid-open No.63-210810, however, has had a disadvantage that it can attain a good imaging quality with difficulty because of its relatively small number of lenses and a simple construction.
The front tele-converter disclosed in Japanese Patent Application Laid-open No.3-59508 also has had a disadvantage that it is of low value in practical use because of its afocal magnification which is as low as about 1.46.
The front tele-converters disclosed in Japanese Patent Publication No.7-119902 and Japanese Patent Application Laid-open No.9-171205 still also have a relatively small number of lenses and a simple construction, also having a low afocal magnification, and can not be said to be high in the basic picture quality itself. In particular, the front tele-converter disclosed in Japanese Patent Publication No.7-119902 has an afocal magnification of as low as about 1.2 at best, and has had a disadvantage that it is of low value in practical use. Also, the front tele-converter disclosed in Japanese Patent Application Laid-open No.9-171205 has a simple construction that its vibration-reduction lens group consists of one negative lens, and hence has had a disadvantage that it can attain a good imaging quality with difficulty.
SUMMARY OF THE INVENTION
As a first basic embodiment of the present invention (hereinafter “first invention”), an object of the present invention is to provide a front tele-converter that may cause less aberrations and has a superior imaging quality though it has a high magnification.
To achieve the above object, the first invention provides a front tele-converter having an afocal magnification higher than 1.9, which is detachably mountable to a photo-taking lens on its object side, wherein;
the front tele-converter has, in order from the object side, a positive lens group GF having a positive refractive power and a negative lens group GR having a negative refractive power;
the positive lens group GF has a positive cemented lens;
the negative lens group GR has a positive lens with its convex surface facing the image side; and
where a focal length of the negative lens group GR is represented by fR, and an effective aperture of a lens surface of the positive lens group GF on its side closest to the object side by &PHgr;F, the lens groups fulfill the condition of:
0.5
<&PHgr;F/|fR|<
10.0
According to a preferred embodiment of the first invention, the positive lens group GF has a positive cemented lens consisting of combination of a negative meniscus lens disposed closest to the object side with its convex surface facing the object side and a positive lens;
the negative lens group GR has a positive lens disposed closest to the object side and a biconcave lens disposed on the image side of the positive lens; and
where a focal length of the positive lens group GF is represented by fF, and an effective aperture of a lens surface of the negative lens group GR on its side closest to the object side by &PHgr;R, the lens groups fulfill the condition of:
0.03
<&PHgr;R/fF<
1.0
According to another preferred embodiment of the first invention, the positive lens group GF is constituted of, in order from the object side, a positive cemented lens consisting of combination of a negative meniscus lens with its convex surface facing the object side and a positive lens, and a positive meniscus lens; and at least one lens of the positive lens and the positive meniscus lens is formed of an optical glass having an Abbe number &ngr;d of 65 or more; and
where a focal length of the positive lens group GF is represented by fF, an afocal magnification of the front tele-converter by M, and an axial gap between the positive lens group GF and the negative lens group GR by DFR, the lens groups fulfill the condition of:
3.0
<fF·M/DFR<
15.0
As a second basic embodiment of the present invention (hereinafter “second invention”), another object of the present invention is to provide a front tele-converter that can well correct various aberrations also at the time of vibration reduction and has a superior imaging quality and a superior vibration-reduction quality, though it has a high magnification.
To achieve the above object, the second invention provides a front tele-converter having vibration-reduction function, having an afocal magnification higher than 1.9, which is detachably mountable to a photo-taking lens on its object side, wherein;
the front tele-converter has, in order from the object side, a positive lens group GF having a positive refractive power and a negative lens group GR having a negative refractive power;
the positive lens group GF has a positive cemented lens;
the negative lens group GR has a cemented lens comprising a positive lens with its convex surface facing the image side;
a vibration-reduction lens group GV comprising a lens group consisting of part or the whole of the negative lens group GR and having a negative refractive power is movable in the direction falling at substantially right angles with the optical axis to effect vibration reduction; and
where the maximum amount of movement of the vibration-reduction lens group GV at the time of vibration reduction, in the direction falling at substantially right angles with the optical axis is represented by &Dgr;S, a focal length of the vibration-reduction lens group GV by fV, and a focal length of the positive lens group GF by fF, the lens groups fulfill the conditions of:
&Dgr;
S/|fV|<
0.2;
and
0.1
<|fV|/fF<
5.0
According to a preferred embodiment of the second invention, where the maximum amount of movement of the vibration-reduction lens group GV in the direction falling at substantially right angles with the optical axis is represented by &Dgr;S, an effective aperture of a lens surface of the positive lens group GF on its side closest to the object side by &PHgr;F, and an effective aperture of a lens surface of the negative lens group GR on its side closest to the object side by &PHgr;R, the lens groups fulfill the condition of:
&Dgr;
S/&PHgr;F<
0.2;
and
2.0
<&PHgr;F/&PHgr;R<
10.0
According to another preferred embodiment of the second invention, the positive lens group GF has a positive cemented lens consisting of combination of a negative meniscus lens disposed closest to the object side and a positive lens;
the negative lens group GR has a positive lens disposed closest to the object side and a biconcave lens disposed on the image side of the positive lens; and
where a focal length of the positive lens group GF is represented by fF, and an effective aperture of a lens surface of the negative lens group GR on its side closest to the object side by &PHgr;R, the lens groups fulfill the condition of:
0.03
<&PHgr;R/fF<
1.0
According to still another preferred embodiment of the second invention, the vibration-reduction lens group GV comprises, in order from the object side, a cemented lens consisting of combination of a positive lens with its convex surface facing the image side and a biconcave lens; and
where an effective aperture of a lens surface of the
Miles & Stockbridge P.C.
Nguyen Thong
Nikon Corporation
LandOfFree
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